There is always a need in the valve industry for a primary valve seal that is reliable in operation over a wide temperature range and irrespective of flow direction. Often manufacturing tolerances have to be kept extremely close in order to ensure integrity of seal throughout the valve service. Some have proposed mechanical biasing means and others have proposed pressure-augmented means to ensure an effective seal. However, such pressure seals tend to retard operation of the valve between open and closed positions.
There is a further need for a fire-safe valve and particularly for some means to effect a reliable seal at elevated temperatures without delaying the effectuation of such seal until after destruction of the primary seal and without suffering the consequences of continual metal to metal contact during normal operation.